Title: Effects of Bi Addition on the Microstructure and Mechanical Properties of Nanocrystalline Ag Coatings

Abstract

Here in this study we investigated the effects of Bi addition on the microstructure and mechanical properties of an electrodeposited nanocrystalline Ag coating. Microstructural features were investigated with transmission electron microscopy (TEM). The results indicate that the addition of Bi introduced nanometer-scale Ag-Bi solid solution particles and more internal defects to the initial Ag microstructures. The anisotropic elastic-plastic properties of the Ag nanocrystalline coating with and without Bi addition were examined with nanoindentation experiments in conjunction with the recently-developed inverse method. The results indicate that the as-deposited nanocrystalline Ag coating contained high mechanical anisotropy. With the addition of 1 atomic percent (at%) Bi, the anisotropy within Ag-Bi coating was very small, and yield strength of the nanocrystalline Ag-Bi alloy in both longitudinal and transverse directions were improved by over 100% compared to that of Ag. On the other hand, the strain-hardening exponent of Ag-Bi was reduced to 0.055 from the original 0.16 of the Ag coating. Furthermore, the addition of Bi only slightly increased the electrical resistivity of the Ag-Bi coating in comparison to Ag. Lastly, results of our study indicate that Bi addition is a promising method for improving the mechanical and physical performances of Ag coating for electricalmore » contacts.« less

@article{osti_1390442,
title = {Effects of Bi Addition on the Microstructure and Mechanical Properties of Nanocrystalline Ag Coatings},
author = {Wang, Yuxin and Cheng, Guang and Tay, See Leng and Guo, Yuxia and Sun, Xin and Gao, Wei},
abstractNote = {Here in this study we investigated the effects of Bi addition on the microstructure and mechanical properties of an electrodeposited nanocrystalline Ag coating. Microstructural features were investigated with transmission electron microscopy (TEM). The results indicate that the addition of Bi introduced nanometer-scale Ag-Bi solid solution particles and more internal defects to the initial Ag microstructures. The anisotropic elastic-plastic properties of the Ag nanocrystalline coating with and without Bi addition were examined with nanoindentation experiments in conjunction with the recently-developed inverse method. The results indicate that the as-deposited nanocrystalline Ag coating contained high mechanical anisotropy. With the addition of 1 atomic percent (at%) Bi, the anisotropy within Ag-Bi coating was very small, and yield strength of the nanocrystalline Ag-Bi alloy in both longitudinal and transverse directions were improved by over 100% compared to that of Ag. On the other hand, the strain-hardening exponent of Ag-Bi was reduced to 0.055 from the original 0.16 of the Ag coating. Furthermore, the addition of Bi only slightly increased the electrical resistivity of the Ag-Bi coating in comparison to Ag. Lastly, results of our study indicate that Bi addition is a promising method for improving the mechanical and physical performances of Ag coating for electrical contacts.},
doi = {10.3390/ma10080932},
journal = {Materials},
number = 8,
volume = 10,
place = {United States},
year = {2017},
month = {8}
}

Silver (Ag) coatings have been widely used in many industry areas due to their excellent conductivity. However, wider applications of Ag coatings have been hindered by their poor mechanical properties. In this research, to improve the mechanical performance, Ag-Bi nano-composite coatings were prepared by a novel ionic co-discharge method. A systematic study of the microstructure, mechanical properties, electrical conductivity and antibacterial behavior of the resulting coating was performed. The results indicated that after adding an appropriate amount of Bi containing solution into the Ag plating solution, Ag-Bi nanoparticles were in-situ formed and distributed uniformly throughout the coating matrix, resulting inmore » a significant improvement in the mechanical properties. The hardness of Ag-Bi coating was increased by 60% compared to that of the pure Ag coating. The corrosion resistance of Ag-Bi coatings was also enhanced. The Ag-Bi coatings prepared in the current study will find a broader application in electronics, jewelry, aerospace and other industries.« less

This project has three main goals: Thin Films Studies, Preparation of Graded Porous Substrates and Basic Electrical Characterization and testing of Planar Single Cells. During this time period substantial progress has been made in developing low temperature deposition techniques to produce dense, nanocrystalline yttrium-stabilized zirconia films on both dense oxide and polymer substrates. Microstructural changes in unsupported nanocrystalline yttrium stabilized zirconia (ZrO{sub 2}:16%Y, or YSZ) thin films were examined as a function of temperature and annealing time in order to determine the grain growth exponent and the mechanisms of pinhole formation. Grain growth and pinhole formation were measured using highmore » resolution transmission electron microscopy (HRTEM), normal imaging mode transmission electron microscopy (TEM), electron diffraction, and energy dispersive X-ray microanalysis (EDS). Grain growth was found to vary with a time exponent of about one half before pinhole formation and about one third after. Pinhole formation in 70 nm thick films occurred at temperatures near 600 C, corresponding to a grain size of about 15 nm, or a grain size to film thickness ration of approximately 0.25. The deposition of films on porous substrates is hampered by the penetration of the polymer precursor solution into the substrate whose pores as > 0.2 {micro}m, therefore much attention has to be paid to the development of porous colloidal oxide films onto surfaces. Thus during this line period we have been studying these films. Optical properties have proven to be an excellent way to study the quality of these nanoporous films. The influence of porosity and densification on optical properties of films on sapphire substrates that were prepared from water colloidal suspensions of small ({approx}5nm) particles of ceria was investigated. The colloidal ceria films have initially very porous structure (porosity about 50%) and densification starts at about 600 C accompanied by grain growth. The concurrence of these two processes makes it difficult to interpret the results of the optical spectrophotometry, but the combination of transmittance and reflectance measurements provides enough data to separate these two influences and to calculate the porosity, particle size and energy band gap separately. XRD, SEM, ellipsometry and mechanical profilometry were used to confirm the results obtained from the spectrophotometric measurements. All these methods gave results, which are in good agreement: the change in the porosity from 50% to 15% and the particle size increased from 5 to 65nm in the temperature region from 400 to 1000 C. An important result of the investigation is the fact that the main optical properties of the coating such as refractive index and band gap energy depend only on the porosity, but not on the grain size. The grain size influences the scattering properties of the coating, which allows the grain size to be estimated from optical measurements.« less

Highlights: • HfTiO{sub 4} thin films were deposited by magnetron co-sputtering. • As-prepared and annealed at 800 °C thin films were nanocrystalline. • Optical properties and hardness were investigated in relation to thin films structure. • Hardness was 3-times higher in the case of as-deposited thin films. • HfTiO{sub 4} thin films are suitable for use as optical coatings with protective properties. - Abstract: Titania (TiO{sub 2}) and hafnium oxide (HfO{sub 2}) thin films are in the focus of interest to the microelectronics community from a dozen years. Because of their outstanding properties like, among the others, high stability, highmore » refractive index, high electric permittivity, they found applications in many optical and electronics domains. In this work discussion on the hardness, microstructure and optical properties of as-deposited and annealed HfTiO{sub 4} thin films has been presented. Deposited films were prepared using magnetron co-sputtering method. Performed investigations revealed that as-deposited coatings were nanocrystalline with HfTiO{sub 4} structure. Deposited films were built from crystallites of ca. 4–12 nm in size and after additional annealing an increase in crystallites size up to 16 nm was observed. Micro-mechanical properties, i.e., hardness and elastic modulus were determined using conventional load-controlled nanoindentation testing. the annealed films had 3-times lower hardness as-compared to as-deposited ones (∼9 GPa). Based on optical investigations real and imaginary components of refractive index were calculated, both for as-deposited and annealed thin films. The real refractive index component increased after annealing from 2.03 to 2.16, while extinction coefficient increased by an order from 10{sup −4} to 10{sup −3}. Structure modification was analyzed together with optical energy band-gap, Urbach energy and using Wemple–DiDomenico model.« less

The objective of this program was to advance the fundamental understanding of thick thermal barrier coating (TTBC) systems for application to low heat rejection diesel engine combustion chambers. Previous reviews of thermal barrier coating technology concluded that the current level of understanding of coating system behavior is inadequate and the lack of fundamental understanding may impede the application of thermal barrier coating to diesel engines.(1) Areas of TTBC technology examined in this program include powder characteristics and chemistry; bond coating composition, coating design, microstructure and thickness as they affect properties, durability, and reliability; and TTBC "aging" effects (microstructural and propertymore » changes) under diesel engine operating conditions. Fifteen TTBC ceramic powders were evaluated. These powders were selected to investigate the effects of different chemistries, different manufacturing methods, lot-to-lot variations, different suppliers and varying impurity levels. Each of the fifteen materials has been sprayed using 36 parameters selected by a design of experiments (DOE) to determine the effects of primary gas (Ar and N2), primary gas flow rate, voltage, arc current, powder feed rate, carrier gas flow rate, and spraying distance. The deposition efficiency, density, and thermal conductivity of the resulting coatings were measured. A coating with a high deposition efficiency and low thermal conductivity is desired from an economic standpoint. An optimum combination of thermal conductivity and disposition efficiency was found for each lot of powder in follow-on experiments and disposition parameters were chosen for full characterization.(2) Strengths of the optimized coatings were determined using 4-point bending specimens. The tensile strength was determined using free-standing coatings made by spraying onto mild steel substrates which were subsequently removed by chemical etching. The compressive strengths of the coatings were determined using composite specimens of ceramic coated onto stainless steel substrates, tested with the coating in compression and the steel in tension. The strength of the coating was determined from an elastic bi-material analysis of the resulting failure of the coating in compression.(3) Altough initial comparisons of the materials would appear to be straight forward from these results, the results of the aging tests of the materials are necessary to insure that trends in properties remain after long term exposure to a diesel environment. Some comparisons can be made, such as the comparison between for lot-to-lot variation. An axial fatigue test to determine the high cycle fatigue behavior of TTBCs was developed at the University of Illinois under funding from this program.(4) A fatigue test apparatus has been designed and initial work performed which demonstrates the ability to provide a routine method of axial testing of coating. The test fixture replaces the normal load frame and fixtures used to transmit the hydraulic oil loading to the sample with the TTBC specimen itself. The TTBC specimen is a composite metal/coating with stainless steel ends. The coating is sprayed onto a mild steel center tube section onto which the stainless steel ends are press fit. The specimen is then machined. After machining, the specimen is placed in an acid bath which etches the mild steel away leaving the TTBC attached to the the stainless steel ends. Plugs are then installed in the ends and the composite specimen loaded in the test fixture where the hydraulic oil pressurizes each end to apply the load. Since oil transmits the load, bending loads are minimized. This test fixture has been modified to allow piston ends to be attached to the specimen which allows tensile loading as well as compressive loading of the specimen. In addition to the room temperature data, specimens have been tested at 800 Degrees C with the surprising result that at high temperature, the TTBC exhibits much higher fatigue strength. Testing of the TTBC using tension/compression cycling has been conducted using the modified test fixture. The goal of this work was to investigate the failure mechanisms of the coating and to determine if tensile and compressive fatigue damage would interact to influence the resulting life of the coating. Coating samples were run with various mean compressive loads and constant tensile loading approximately equal to 90% of the tensile strength of the coating. The results of this testing shows no interaction of failure resulting from the tensile and compressive load. The material fails in tension at the life predicted by the maximum tensile stress or in compression at the life predicted by the compressive stress. This indicates that there are two differing failure mechanisms for the TTBC in tension and compression.« less

A number of nanocrystalline ceramics have been fabricated by the gas phase condensation technique. The mechanical properties of one of the first ceramics produced by this method, nanophase TiO{sub 2},have been discussed in an earlier study. This paper reports a similar study undertaken to examine the properties of nanocrystalline ZnO. Nanoindenter techniques are used to determine hardness, Young's modulus, and strain rate sensitivity in ultra-fine grained ZnO. Significant properties variations are experienced within a given sample, indicating a large degree of microstructural inhomogeneity. Nevertheless, a distinct evolution in properties can be observed as a function of sintering temperature. Young's modulusmore » and hardness values increase almost linearly with increasing sintering temperature, and, in addition, there also appears to be a linear correlation between the development of the two materials properties. In contrast, strain rate sensitivity is shown to have an inverse dependence on sintering temperature. This dependence appears to be linked to the strong influence of grain size on strain rate sensitivity, so that the lower sintering temperatures, which provide the finer grain sizes, tend to promote strain rate sensitivity. The results of this study are strikingly similar to those obtained earlier for nanophase TiO{sub 2}, and they indicate that the earlier results could probably be generalized to a much broader range of nanocrystalline ceramics.« less